Method to improve adhesion of photoresist on silicon substrate for extreme ultraviolet and electron beam lithography

ABSTRACT

An etch process that includes removing an oxide containing surface layer from a semiconductor surface to be etched by applying a hydrofluoric (HF) based chemistry, wherein the hydrofluoric (HF) based chemistry terminates the semiconductor surface to be etched with silicon-hydrogen bonds, and applying a vapor priming agent bearing chemical functionality based on the group consisting of alkynes, alcohols and a combination thereof to convert the silane terminated surface to a hydrophobic organic surface. The method continues with forming a photoresist layer on the hydrophobic organic surface; and patterning the photoresist layer. Thereafter, the patterned portions of the photoresist are developed to provide an etch mask. The portions of the semiconductor surface exposed by the etch mask are then etched.

BACKGROUND Technical Field

The present invention generally relates to lithographic materials forextreme ultraviolet (EUV) and electron beam (E-beam) lithography, andmore particularly to inorganic hardmask processing used in EUVlithography.

Description of the Related Art

Semiconductor fabrication typically involves transfer of a pattern froma mask to a resist using lithography, and transfer of the pattern fromthe resist to a hardmask through etching. The pattern can then betransferred from the hardmask to a semiconductor material throughfurther etching processes. In general, photolithography (in contrast toe-beam lithography, for example) uses light to form an image of the maskon a photoresist material, where the incident light can cause a photoreaction. Light for photolithography has progressed from wavelengths inthe range of 436 nm (blue light) to 365 nm (near ultraviolet (UV)) to248 nm (deep UV) to a wavelength of 193 nm. The wavelength of light hasmoved to smaller and smaller wavelengths in part because the smallestfeature size that can be printed is determined in part by thewavelength, λ, of the light used. Another factor that can affect thesmallest printed feature size is the numerical aperture, NA, of theprojection optics. The depth-of-focus (DOF) is also determined by A andthe numerical aperture NA, which is also typically a factor in resolvingsmall features. The DOF can relate to a visible change in the imagerelated to exposure dose, line width, sidewall angle, and resist loss.As feature sizes decrease, their sensitivity to focus errors increases.

In extreme ultraviolet lithography (EUVL) the extreme ultraviolet light(which also may be referred to as soft x-ray) has wavelengths from 124nm down to 10 nm, and in particular for intended semiconductorprocessing, about 13.5 nm, as generated by a laser-pulsed tin (Sn)plasma source. The 13.5 nm EUV light is currently the focus of the nextgeneration of photolithography tools and processes.

Electron-beam lithography (often abbreviated as e-beam lithography) isthe practice of scanning a focused beam of electrons to draw customshapes on a surface covered with an electron-sensitive film called aresist (exposing). The electron beam changes the solubility of theresist, enabling selective removal of either the exposed or non-exposedregions of the resist by immersing it in a solvent (developing). Oneadvantage of electron-beam lithography is that in some examples it candraw custom patterns (direct-write) with sub-10 nm resolution.

High resolution patterning using Extreme Ultraviolet (EUV) lithographyis typically carried out with a combination of dark field masks and EUVresists utilizing positive tone development (PTD). Among the differentfamilies of positive tone EUV resists, chemically amplified resists is acommon material platform, using aqueous tetramethylammonium hydroxide(TMAH) in the PTD step. In some examples, for the subsequent imagetransfer of the EUV patterned structures into the underlying stack usingreactive ion etch (RIE), a silicon-based hardmask layer directly locatedunder the EUV resist is used in combination with selective etchprocessing. This hardmask can be a spin-on hybrid material, e.g.silicon-containing organic layer, or a vacuum-deposited inorganic layersuch as polycrystalline silicon (p-Si) or amorphous silicon (α-Si). Insome instances, high silicon content is associated with high etchselectivity. Therefore, the vacuum-deposited inorganic layers, such aspolycrystalline silicon (p-Si) or amorphous silicon (α-Si) are oftenemployed.

However, these materials are characterized by the presence of a nativesurface oxide layer (SiO_(x)) about 1 nm thick. The EUV resiststructures feature poor adhesion to the silicon layer due to the acidicnature of the silanol (SiOH) termination of the SiO_(x) surface layer.Typically, a surface priming process that replaces the hydrophilic SiO—Hwith a hydrophobic SiO—Si(CH₃)₃ termination is carried out utilizingvapor-applied hexamethyldisilazane (HMDS), which can improved adhesionof the EUV resist pattern to the silicon layer underneath.

However, the standard HMDS vapor priming process is insufficient atimproving the adhesion of high resolution EUV patterns, such astightly-pitched sub-20 nm EUV resist lines. Therefore, a method isneeded to improve the adhesion of EUV photoresists to the siliconhardmask.

SUMMARY

The methods and structures described herein provide for improving theadhesion of high resolution EUV patterns over the insufficient adhesionproperties of prior methods that employ hexamethyldisilazane (HMDS)vapor priming. In some embodiments, the methods disclosed herein canstrip the top surface oxide layer (SiOx) from a provided silicon layerwith diluted hydrofluoric acid (dHF) to generates silane (SiH)terminated silicon surface. In some embodiments, a vapor priming agentis provided bearing chemical functionality based on alkynes (C—C triplebond), alcohols (ROH), or the combination thereof to the SiH-terminatedSi layer to form a hydrophobic organic surface. The EUV resist adhesionpromotion methods that are described herein provide improved patterningfidelity on silicon hardmask during TMAH development.

In one embodiment, a patterning method that can be suitable for EUVlithography or E-beam lithography, in which the method includesproviding a semiconductor surface to be patterned; and removing an oxidecontaining surface layer from the semiconductor surface that is to bepatterned with a hydrofluoric (HF) based chemistry, wherein applying theHF base chemistry to the surface to be patterned forms a silaneterminated surface. Thereafter, the method continues with the applying avapor priming agent bearing chemical functionality based on alkynes toconvert the silane terminated surface to a hydrophobic organic surface.A photoresist may then be formed on the hydrophobic organic surface tobe patterned, and the photoresist can be patterned. In a following step,the photoresist is developed on the surface to be patterned usingpositive and/or negative tone development (NTD).

In another embodiment, a patterning method that can be suitable for EUVlithography or E-beam lithography, in which the method includesproviding a semiconductor surface composed of a type IV semiconductormaterial to be patterned; and removing an oxide containing surface layerfrom the semiconductor surface that is to be patterned with an HF basechemistry, wherein applying the HF base chemistry to the surface to bepatterned forms a silane terminated surface. Thereafter, the methodcontinues with the applying a vapor priming agent bearing chemicalfunctionality based on alcohols to convert the silane terminated surfaceto a hydrophobic organic surface. A photoresist may then be formed onthe hydrophobic organic surface to be patterned, and the photoresist canbe patterned lithographically using an extreme ultra violet (EUV)method. In a following step, the photoresist is developed on the surfaceto be patterned using positive and/or negative tone development (NTD).

In another aspect, an etch process that can be suitable for EUVlithography or E-beam lithography is provided that in one embodiment caninclude providing a semiconductor surface to be etched; and removing anoxide containing surface layer from the semiconductor surface to beetched by applying a hydrofluoric (HF) based chemistry, wherein thehydrofluoric (HF) based chemistry terminates the semiconductor surfaceto be etched with silicon-hydrogen bonds. Thereafter, the methodcontinues with the applying a vapor priming agent bearing chemicalfunctionality based on the group consisting of alkynes, alcohols and acombination thereof to convert the silane terminated surface to ahydrophobic organic surface. A photoresist may then be formed on thehydrophobic organic surface to be patterned, and the photoresist can bepatterned lithographically using an extreme ultra violet (EUV) method.In a following step, the photoresist is developed on the surface to bepatterned using positive and/or negative tone development (NTD).Thereafter, the method continues with etching the portions of thesemiconductor surface exposed by the mask, while the portions of thesemiconductor surface that are underlying the mask are not etched.

These and other features and advantages will become apparent from thefollowing detailed description of illustrative embodiments thereof,which is to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description will provide details of preferred embodimentswith reference to the following figures wherein:

FIG. 1 is a flow diagram illustrating one embodiment of an etch methodusing the photolithography process that includes the steps of removingan oxide containing surface layer from the semiconductor surface that isto be patterned with a hydrofluoric (HF) based chemistry, and applying avapor priming agent bearing chemical functionality based on alkynesand/or alcohols to convert the silane terminated surface to ahydrophobic organic surface, in accordance with one embodiment of thepresent disclosure.

FIG. 2 is a side cross-sectional view depicting one embodiment ofproviding a semiconductor surface to be etched, and terminating theamorphous semiconductor surface by forming silicon-hydrogen (Si—H)bonds. i.e., silane terminated surface, on the surface to be patterned,in accordance with one embodiment of the present disclosure.

FIG. 3 is an illustration depicting the surface reactions that occur atthe semiconductor surface to be etched in accordance with one embodimentof the method described herein.

FIG. 4 is a side cross-sectional view depicting applying a vapor primingagent bearing chemical functionality based on alkynes and/or alcohols toconvert the silane terminated surface to a hydrophobic organic surface,in accordance with one embodiment of the present disclosure.

FIG. 5 is a list of vapor priming agents based on alkynes and/oralcohols, suitable for the conversion of a silane terminated surfaceinto a hydrophobic organic surface, in accordance with one embodiment ofthe present disclosure.

FIG. 6 is a side cross-sectional view depicting forming a photoresist onthe surface to be patterned.

FIG. 7 is a side cross-sectional view depicting lithographicallypatterning the photoresist layer using an extreme ultra violet (EUV)method.

FIG. 8 is a side cross-sectional view depicting a photoresist beingdeveloped into a mask on the surface to be patterned.

FIG. 9 is a scanning electron microscope (SEM) image of a developedresist that was formed on an amorphous silicon surface that was treatedwith a dilute hydrofluoric acid (dHF) rinse followed by applying a vaporpriming agent bearing chemical functionality based on alkynes and/oralcohols to convert the silane terminated surface to a hydrophobicorganic surface prior to forming the photoresist layer, in accordancewith one embodiment of the present disclosure.

FIG. 10 is a side cross-sectional view depicting one embodiment ofetching the exposed portions of the amorphous semiconductor surface,while the portions of the amorphous semiconductor layer that areunderlying the mask are not etched.

DETAILED DESCRIPTION

Principles and embodiments of the present invention relate generally tofabricating microelectronics structures, and the resulting structuresformed thereby, using extreme ultraviolet (EUV) lithographic andelectron beam (E-beam) processes. Patterning of small features generatedby extreme ultraviolet (EUV) and E-beam lithography can be limited by avariety of factors, from the photoresist over the substrate to thedeveloper.

The methods and structures described herein provide for improvedadhesion promotion for photoresist material layers used in EUV andR-beam lithography. In some embodiments, the method includes strippingthe top surface oxide layer, e.g., silicon oxide (SiO_(x)) layer, from asilicon containing layer, or other type IV semiconductor surface, with ahydrofluoric containing chemistry, such as diluted hydrofluoric acid(dHF), to generate a silane (SiH) terminated silicon surface anddelivering a vapor priming agent bearing chemical functionality based onalkynes (C—C triple bond), alcohols (ROH), or a combination thereof tothe SiH-terminated Si layer to form a hydrophobic organic surface. Ithas been determined that in some embodiments the formation of thehydrophobic organic surface promotes resist adhesion, and providesimproved patterned fidelity, e.g., provides improved EUV resist adhesionand provides improved patterning fidelity on silicon hardmask duringTMAH development when compared to prior methods that employ surfacepriming with hexamethyldisilazane (HMDS). The patterning/etchingprocesses for EUV and E-beam lithography that employ the above describedadhesion/fidelity promotion schemes are now described with more detailwith reference to FIGS. 1-11.

In some embodiments, the method can begin with providing a semiconductorsurface 10 to be etched, and terminating the semiconductor surface byforming silicon-hydrogen (Si—H) bonds 15 on the surface to be patternedat Step 1 of the process flow depicted in FIG. 1, as illustrated in FIG.2. In some embodiments, the semiconductor surface 10 may be provided byan amorphous semiconductor material. The term “amorphous” denotes thatthe semiconductor material does not have a regular repeating crystallinestructure. In some examples, the semiconductor surface 10 may beentirely amorphous, e.g., amorphous silicon (α-Si), and may also includean amorphous matrix with islands of crystalline material, such as inmicrocrystalline silicon or nanocrystalline silicon. Although FIG. 2depicts that the semiconductor surface 10 is an independent layer, otherembodiments have been contemplated in which the semiconductor surface 10is a component of a material stack of other semiconductor materials,such as type IV and type III-V semiconductor materials, that may havecrystalline, e.g., single crystalline, or amorphous crystal structures;or the semiconductor surface 10 may be present atop a supportingsubstrate, which may be composed of a semiconductor material, e.g., typeIV and/or type III-V. It is not required that the supporting substratebe composed of semiconductor material, as other dielectric materials,such as oxides, nitrides and glass compositions, and metal materials maybe suitable for providing a supporting substrate for the semiconductorsurface 10. In some examples, the supporting substrate for thesemiconductor surface 10 may be a polymeric material.

The semiconductor surface 10 typically includes a “native oxide”. Theterm “native oxide” can refer to an oxide containing layer that forms onthe semiconductor surface 10 from its exposure to air or other oxygencontaining atmosphere. The native oxide is typically a thin layer, whichcan be on the order of 2 nm or less in thickness, in some instancesbeing less than 1 nm in thickness. In some examples, when thesemiconductor surface 10 is composed of silicon (Si), the native oxidemay be a silicon oxide containing layer, e.g., silicon oxide (SiO₂).

At step 1 of the process flow that is described in FIG. 1, the nativeoxide that is present on the semiconductor surface 10 is typicallyremoved by applying a hydrofluoric (HF) based chemistry 16 thatterminates the semiconductor surface 10 to be etched with siliconhydrogen (Si—H) bonds 15, as depicted in FIG. 2. In some embodiments,prior to applying the dilute hydrofluoric acid (dHF) rinse 16, thesemiconductor surface 10 may be cleaned using one of acetone, methanol,and deionized water. In some embodiments, when the semiconductor surface10 is composed of amorphous silicon (α-Si), the semiconductor surface 10can be treated with a wet chemical rinse of a hydrofluoric (HF)containing chemistry 16, e.g., a dilute hydrofluoric acid (dHF)composition 26, which terminates the amorphous silicon with hydrogen tosilicon (Si—H) bonding. It is noted that prior to being terminated withsemiconductor-hydrogen bonding, e.g., silicon-hydrogen (Si—H) bonding,the dilute HF rinse may remove any naturally forming oxide, e.g.,silicon oxide, that may be present on the semiconductor surface 10.

FIG. 3 illustrates the native oxide 11 that is present on thesemiconductor surface 10, in which the native oxide 11 may include anhydroxide (OH) functionalized surface 12. FIG. 3 further depicts thatthe application of the hydrofluoric (HF) containing chemistry 16. e.g.,dilute hydrofluoric acid (dHF), removes the native oxide, and convertsthe hydroxide (OH) functionalized surface 12 to a silane functionalizedsurface 15 a, which includes silicon hydrogen (Si—H) bonds 15. In theexample that is depicted in FIG. 3, the semiconductor surface 10 may beamorphous silicon (α-Si), and the hydrofluoric (HF) containing chemistrymay be dilute hydrofluoric acid (dHF).

In one example, the dilute hydrofluoric acid (dHF) rinse that is used toremove the native oxide 11, and terminate the semiconductor surface 10with silicon-hydrogen (Si—H) bonds 15, i.e., form a silane terminatedsurface, can include a very highly diluted HF mixture, e.g., less than0.1%. The dilute hydrofluoric (dHF) acid rinse is an aqueous solution.It is noted that the previous example of a 0.1% diluted HF mixture isonly one example of a diluted HF (dHF) rinse that is suitable forterminating the amorphous semiconductor layer 10. For example, thedilute HF (dHF) rinse may include hydrofluoric acid (dHF) in amountsequal to 10%, 5%, 3%, 1%, 0.5%, 0.3%, 0.1%, 0.09%, 0.08%, 0.07%, 0.06%,0.05%, 0.04%, 0.03%, 0.02%, 0.01%, as well as any range including one ofthe aforementioned examples for the maximum value of the range, and oneof the aforementioned examples for the minimum value of the range. It isnoted that the HF-based chemical is not limited to only theaforementioned dHF solution. For example, in some embodiments theHF-based chemical may be a buffered hydrofluoric acid (BHF) solution,which is a mixed solution of dHF and NH₄F.

The HF-based chemical, e.g., dilute hydrofluoric acid (dHF) rinse, maybe applied by dipping the semiconductor surface 10 into a dHF bath. Inother embodiments, the dilute hydrofluoric acid (dHF) rinse may beapplied by pouring, e.g., via curtain pouring, the dHF onto thesemiconductor surface 10. In yet other embodiments, the dilutehydrofluoric acid (dHF) rinse is applied by spray and/or brush.

The application of the HF-based chemical, e.g., dilute HF (dHF) rinse,may be at room temperature, e.g., 20° C. or 25° C. at 1 atm. In someembodiments, the temperature for the application of the HF-basedchemical, e.g., dilute HF (dHF) rinse, may be at a temperature elevatedfrom room temperature. For example, in some instances, the temperaturefor the application of the HF-based chemical, e.g., dilute HF (dHF)rinse, can range from 70° C. to 80° C.

Because the native oxide 11, e.g. silicon oxide (SiO₂), that is presenton the semiconductor surface 10 is relatively thin. e.g., less than 1nm, the concentration of the HF-based chemistry may be dilute, e.g.,dHF, and the time period for the application of the HF-based chemical,e.g., dHF, may be relatively short. For example, the processing time forthe application of the HF-based chemical, e.g., dHF, that removes thenative oxide and terminates the semiconductor surface 10 may be appliedfor a time period of 1 minute or less. It is noted that the aboveexample is provided for illustrative purposes only, and is not intendedto limit the present disclosure. For example, the application time forthe HF-based chemical, e.g., dilute HF (dHF) rinse, may be equal to 5seconds, 15 seconds, 30 seconds, 1 minute, 2 minutes, 3 minutes, 5minutes, 10 minutes, 15 minutes, 30 minutes and 1 hour, as well as anyrange including one of the aforementioned examples for the maximum valueof the range, and one of the aforementioned examples for the minimumvalue of the range.

Following application of the HF-based chemical, e.g., dHF, that removesthe native oxide and terminates the semiconductor surface 10 withsilicon-hydrogen (Si—H) bonds, the now terminated semiconductor surface10 may be rinsed with deionized water. In some examples, any acidity maybe neutralized using a more basic composition to neutralize and rinsethe terminated surface.

Stripping the native oxide 11 with a HF-based chemical rinse, such asdHF, converts the terminal surface functionality from polar (Si—OH) tonon-polar (Si—H). It is noted that termination of the semiconductorsurface 10 can form silicon-hydrogen (Si—H) bonds in the form of Si—H,≡SiH, ═SiH₂, —SiH₃, or a combination thereof. Silane terminated (Si—H)surfaces are non-polar. However. Si—H bonds react with aqueous bases,such as tetramethylammonium hydroxide (TMAH) developer. It has beendetermined that TMAH developer can lift off photoresist patterns,particularly small features, in the development stage of the lithographyprocess.

To overcome the effects of tetramethylammonium hydroxide (TMAH)developer on the non-polar silicon hydrogen (Si—H) bond termination thatresults from the reaction of the hydrofluoric containing chemistry,e.g., dilute hydrofluoric acid, with the semiconductor surface 10, themethod continues with priming the Si—H terminated surface with alkynes,alcohols or a combination thereof at step 2 of the process flow depictedin FIG. 1. Referring to FIG. 4. In some embodiments, the method cancontinue with delivering a vapor priming agent 17 a, 17 b based onalkynes (C—C triple bond), alcohols (ROH), or a combination thereof toconvert the silane (Si—H) terminated surfaces to a hydrophobic organicsurface, i.e., polar surface. The term “hydrophobic” means tending torepel or fail to mix with water. The term “hydrophilic” refers to asurface having a strong affinity for water. An “alkyne” is anunsaturated hydrocarbon containing at least one carbon-carbon triplebond. Examples of alkynes based priming agents 17 a include5-chloro-1-pentyne (reference numeral XVI). Propargyl ether (referencenumeral XVII). Iodo-1-pentyne (reference numeral XVIII), 5-Hexynoic acid(reference numeral XIX), 1,7-Octadiyne (reference numeral XX). Ethylpropiolate (reference numeral XXI), Dimethyl propargylmalonate(reference numeral XXII), Methyl propiolate (reference numeral XXIII),1-Hexyne (reference numeral XXIV), 1-Octyne (reference numeral XXV),3-Chloro-1-propanol (reference numeral XXVI), and combinations thereof,in which roman numerals are used to correlate the chemical structuralillustrated in FIG. 5 to the aforementioned examples. An alcohol is anyorganic compound in which the hydroxyl functional group (—OH) is boundto a saturated carbon atom. Examples of alcohol based priming agents 17b include 2-Propyn-1-ol (reference numeral I), 3-Butyn-1-ol (referencenumeral II), 4-Pentyn-1-ol (reference numeral III), 1-Hexyn-3-ol(reference numeral IV), 4-Pentyn-2-ol (reference numeral V),1-Pentyn-3-ol (reference numeral VI), 4-Methyl-1-heptyn-3-ol (referencenumeral VII), 5-Hexyn-3-ol (reference numeral VIII), 1-Octyn-3-ol(reference numeral IX), 3-Butyn-2-ol (reference numeral X),3,5-Dimethyl-1-hexyn-3-ol (reference numeral XI), 2-Methyl-3-butyn-2-ol(reference numeral XII), 3-Methyl-1-pentyn-3-ol (reference numeralXIII), 3-Ethyl-1-pentyn-3-ol (reference numeral XIV),1-Ethynylcyclopentanol (reference numeral XV), and combinations thereof,in which roman numerals are used to correlate the chemical structuralillustrated in FIG. 5 to the aforementioned examples. It is noted thatthe above examples are illustrative and not limiting. Suitable alkynes,alcohols and alkyn-ols are those which are liquids at room temperature(melting point below 20 C) and have a boiling point below 250 C, mostpreferable between 120° and 170° C., in order to provide sufficientvapor pressure and maintain the flash point above 100° F. (37° C.).

The vapor priming agent 17 a, 17 b based on alkynes (C—C triple bond),alcohols (ROH), or a combination thereof is typically applied using aspray method, but in other instances, the vapor priming agent 17 a, 17 bmay be applied using a curtain deposition method. Although the primingagent is described as a vapor the present disclosure is not limited toonly this example. For example, the priming agent (having thecompositions listed above and depicted in FIG. 5) may also be applied tothe surface to be patterned in liquid form, using spraying, dipping,brushing and curtain coating methods.

The vapor priming agent 17 a, 17 b may be applied using a carrier gassuch as nitrogen (N₂) carrier gas. Other carriers gasses that may besuitable for use with the methods described herein can include hydrogen,helium, argon and combinations thereof.

The temperature for the vapor priming agent 17 a, 17 b may beapproximately room temperature, e.g., ranging from 20° C. to 25° C., at1 ATM. In some instances, raising the temperature at which the vaporpriming agent 17 a, 17 b is applied can decrease the application time.In some embodiments, the vapor priming agent 17 a, 17 b is applied at atemperature ranging from 50° C. to 250° C., for a time period rangingfrom 5 seconds to 5 hours. In another embodiment, the vapor primingagent 17 a, 17 b is applied at a temperature ranging from 100° C. to200° C., for a time period ranging from 1 minute to 5 minutes. In yetanother embodiment, the vapor priming agent 17 a, 17 b is applied at atemperature ranging of 150° C., for a time period ranging from 1 minuteto 5 minutes.

Referring to FIGS. 3 and 4, the vapor priming agent 17 based on alkynes(C—C triple bond), alcohols (ROH), or a combination thereof when appliedto the surface of the semiconductor surface 10 reacts with thesilicon-hydrogen bonds so that the alcohols and alkynes react with thesilicon-hydrogen bonds to form a chemical bond, which in someembodiments can be as follows:

As depicted in FIGS. 3 and 4, in some embodiments, the terminal siliconis capped and becomes resistant to base attack. The product produced byreaction of the vapor priming agent based on alkynes (C—C triple bond)17 a that reacts with the Si—H bonded surface is identified by referencenumber 17 a′. The product produced by reaction of the vapor primingagent based on alcohol (—OH) 17 b that reacts with the Si—H bondedsurface is identified by reference number 17 b′. The terminal siliconhas been capped and becomes resistant to base attack. In someembodiments, the organic pendant groups can be tailored to match, ormismatch, a photoresist to be coated onto it. The reaction provided bythe vapor priming agent 17 based on alkynes (C—C triple bond), alcohols(ROH), or a combination thereof when applied to the surface of thesemiconductor surface 10 reacts with the silicon-hydrogen bonds toprovide a hydrophobic organic surface that can significantly improveresist adhesion during development using tetramethylammonium hydroxide(TMAH) or like developers, such as those used during positive toneresist development and/or negative tone resist development.

Referring to FIG. 1, the method may continue with forming a forming aphotoresist layer 20 on the semiconductor surface 10 to be patterned atstep 3, as depicted in FIG. 6. The photoresist layer 20 that isdeposited is suitable for positive tone development (PTD), but in someembodiments the methods disclosed herein are equally applicable tonegative tone development (NTD). The image of the mask features isintended to be transferred to a photoresist on the substrate. Typically,in positive tone photoresist development the exposed area, i.e., areaexposed to lithographic radiation, is made soluble in the developer. Innegative tone photoresist development the exposed area. i.e., areaexposed to lithographic radiation, is made insoluble to the developer.The process flow described herein is suitable for photoresist materialsthat are developed using tetramethylammonium hydroxide (TMAH), or atetramethylammonium hydroxide (TMAH) like developer. Therefore, anyphotoresist, whether a positive tone resist (PTR) or negative toneresist (NTR) may benefit from the improved adhesion provided by themethod described herein for use with tetramethylammonium hydroxide(TMAH) or tetramethylammonium hydroxide (TMAH) like developers. In someembodiments, photoresists that can provide the photoresist layer 20 maybe phenolic, acrylic or hybrid (phenolic-acrylic) chemically amplifiedphotoresists.

In a first embodiment, a phenolic photoresist layer 20 is provided thatcan be a copolymer of polyhydroxystyrene modified with a ketal-basedprotecting group or a tert-butyloxycarbonyl protecting group. Thephenolic photoresist layer 20 can be formulated by dissolution of thephenolic resin, a suitable photoacid generator such astriphenylsulfonium perfluorobutanesulfonate and a base quencher such astetrabutylammonium lactate in an organic solvent such as propyleneglycol monomethyl ether acetate. The thickness of the deposited layermay be smaller than 100 nm. For example, the thickness of the depositedphotoresist layer 20 may range from 50 nm to 30 nm in order to make itsuitable for high resolution patterning, i.e., for the patterning ofsub-40 nm pitched structures.

In another embodiment, an acrylic photoresist layer 20 is suitable foruse with the methods described herein, wherein the acrylic photoresistlayer 20 can be a copolymer of norbornane lactone methacrylate (NLM) andmethyl adamantane methacrylate (MAdMA). The acrylic photoresist layer 20can be formulated by dissolution of the acrylic resin, a suitablephotoacid generator such as triphenylsulfonium perfluorobutanesulfonate,and a base quencher, such as tetrabutylammonium lactate in an organicsolvent such as cyclohexanone. The thickness of the deposited layer maybe smaller than 100 nm. For example, the thickness of the depositedphotoresist layer 20 may range from 30 nm to 50 nm in order to make itsuitable for high resolution patterning. i.e., for the patterning ofsub-40 nm pitched structures.

In another embodiment, a hybrid photoresist layer 20 can be a copolymerof polyhydroxystyrene and methyl adamantane methacrylate (MAdMA). Thehybrid photoresist layer 20 can be formulated by dissolution of thehybrid resin, a suitable photoacid generator such as triphenylsulfoniumperfluorobutanesulfonate and a base quencher such as tetrabutylammoniumlactate in an organic solvent such as propylene glycol monomethyl etheracetate. The thickness of the deposited layer may be smaller than 100nm. For example, the thickness of the deposited photoresist layer 20 mayrange from 50 nm to 30 nm in order to make it suitable for highresolution patterning, i.e., for the patterning of sub-40 nm pitchedstructures.

It is noted that the above examples of photoresist compositions areprovided for illustrative purposes only, and are not intended to limitthe present disclosure. Other compositions for photoresists are alsoapplicable to the present disclosure including polymers, such aspolycarbonates, polyimides, polyesters, polyalkenes, copolymers thereofand combinations thereof.

In general, any suitable coating process can be used to deliver thephotoresist layer 20 to the semiconductor surface that has been treatedusing a vapor priming agent based on alkynes (C—C triple bond), alcohols(ROH), or a combination thereof. Suitable coating approaches caninclude, for example, spin coating, spray coating, dip coating, knifeedge coating, printing approaches, such as inkjet printing and screenprinting, and the like. Some of these coating approaches form patternsof coating material during the coating process, although the resolutionavailable currently from printing or the like has a significantly lowerlevel of resolution than available from radiation based patterning asdescribed herein. The coating material can be applied in multiplecoating steps to provide greater control over the coating process. Forexample, multiple spin coatings can be performed to yield an ultimatecoating thickness desired. The thickness of the deposited layer mayrange from 1 nm to 500 μm. In some embodiments, the photoresist has athickness of less than 50 nm.

In one embodiment, the photoresist layer 20 may be deposited using spinon deposition methods, in which the spin rate for the substrate mayrange from 500 rpm to 10.000 rpm.

Following deposition of the photoresist layer 20, the method maycontinue with heating or evaporation of the solvent to harden thephotoresist layer. The coating process itself can result in theevaporation of a portion of the solvent since many coating processesform droplets or other forms of the coating material with larger surfaceareas and/or movement of the solution that stimulates evaporation. Theloss of solvent tends to increase the viscosity of the coating materialas the concentration of the species in the material increases. Ingeneral, the coating material can be heated prior to radiation exposureto further drive off solvent and promote densification of the coatingmaterial.

While heating is not needed for successful application of the process,it can be desirable to heat the coated substrate to speed the processingand/or to increase the reproducibility of the process. In embodiments inwhich heat is applied to remove solvent, the coating material can beheated to temperatures from 45° C. to 150° C. in further embodimentsfrom 50° C. to 130° C. and in other embodiments from 60° C. to 110° C.The heating for solvent removal can generally be performed for at leastabout 0.1 minute, in further embodiments from about 0.5 minutes to about30 minutes and in additional embodiments from about 0.75 minutes toabout 10 minutes. This heating process may be referred to as post-applybake (PAB).

Referring to FIG. 1, following formation of the photoresist layer 20,the method may continue with lithographically patterning the photoresistlayer using an extreme ultra violet (EUV) method at step 4, asillustrated in FIG. 7. In some examples, a pattern is formed using areticle or photomask 25 and transferred into the photoresist layer 20.Light is reflected off the multi-mirrored surface of the reticle, whichin turn produces a patterned image on the layer of photoresist. Forexample, exposure to light may change the exposed portions 20 a of thephotoresist from an insoluble condition to a soluble one, as in the caseof positive tone resist. The exposed portion 20 b of the photoresist isdissolved by the photoresist developer.

The light source 30 may be an EUV light source. EUV light sourcesdesigned for lithography tools typically have high average power (e.g.,100 W and above) at 2% bandwidth with a central wavelength of 13.5 nm.Such systems typically employ a laser produced plasma (LPP) with a metaltarget (e.g., Sn) and a high power laser (e.g., CO₂ with wavelength of10.6 μm). Such a combination is well suited for achieving highconversion efficiency (up to 4-5% in band) and high average power (about100 W and above). In some embodiments to provide an EUV light source, alaser source is provided for initiating and/or maintaining a plasma. Inthis regard, the laser source may supply the energy required to rapidlyheat the plasma-forming target material to a plasma, which, in turn,emits EUV light, i.e., the light source 30.

In one embodiment, the drive laser source may include, but is notlimited to, one or more drive lasers. The number and type of lasers usedin the drive laser source may depend on a number of factors including,but not limited to, the required power output of the individual lasers,the desired EUV light power output, and the efficiency of the EUV lightgeneration process. As an example, EUV light is used by photolithographymask inspection systems, but such systems do not require the high EUVlight power output of primary photolithography systems. An EUV maskinspection system may only require EUV light in the range of 10 W, butwith high brightness in a small area. In the case of mask inspectionsystems, total laser output in the range of a few kilowatts is needed,with the output being focused onto a small target spot (e.g., less than100 μm in diameter).

The drive source may include any pulsed or modulated illumination sourceknown in the art. For example, the drive laser source may include, butis not limited to, a pulsed laser. In one embodiment, the drive lasersource may include, but is not limited to, one or more solid statelasers. For example, the drive laser source may include, but is notlimited to, one or more Nd:YAG, Er:YAG. Yb:YAG. Ti:Sapphire,Nd:Vanadate, and like lasers. In another embodiment, the drive lasersource may include, but is not limited to, a gas-discharge laser. Forexample, the drive laser source may include, but is not limited to, oneor more excimer lasers. In another embodiment, the drive laser sourcemay include, but is not limited to, any laser system capable of emittinglight having a wavelength less than 1 μm.

In one embodiment, the one or more laser pulses of beam to provide thelight source 30 may include a train of pulses with duration in the rangeof 5 to 50 ns. In another embodiment, the total average power of thebeam outputted by the laser source may be in the range of 1-10 kW. Inanother embodiment, the combination of multiple laser outputs mayinclude triggering multiple lasers synchronously.

Although the light source 30 used for patterning the photoresist istypically an EUV light source, the methods disclosed herein are alsoapplicable to immersion photolithography. e.g., 193 nm lithography, aswell as e-beam lithography.

Referring to FIG. 1, following lithographically patterning thephotoresist layer 20, 20 a, 20 b, the method may continue with a hardbake. In general, the coating material can be heated post-radiationexposure to catalyze the cleavage of the protective group from thephotoresist layer 20 in order to promote the desired solubility switch.This heating process may be referred to as post-exposure bake (PEB).

In embodiments in which heat is applied to drive the deprotectionreaction of the chemically amplified resist, the coating material can beheated to temperatures from 45° C. to 150° C., in further embodimentsfrom 50° C. to 130° C. and in other embodiments from 60° C. to 110° C.The post-exposure bake (PEB) can generally be performed for at leastabout 0.1 minute, in further embodiments from about 0.5 minutes to about30 minutes and in additional embodiments from about 0.75 minutes toabout 10 minutes. Referring to FIG. 1, following post-exposure baking ofthe photoresist layer 20, 20 a, 20 b, the method may continue with adevelopment step that removes the portions of the photoresist layer 20 athat were exposed selectively to the unexposed portions of photoresistlayer 20 b at step 5, as illustrated in FIG. 8. Development of the imageinvolves the contact of the patterned photoresist layer 20 including thelatent image to a developer composition 35 to remove the irradiatedphotoresist portions 20 a.

In one embodiment, the developer composition 35 can be tetramethylammonium hydroxide (TMAH). Commercial TMAH is available at 2.38 weightpercent, and this concentration can be used for the processing describedherein. However, in some embodiments, the developer composition 35 canbe delivered at higher concentrations relative to the concentrationsgenerally used for the development of organic resists, such as 25% byweight TMAH. The developer can be applied to the patterned coatingmaterial using any reasonable approach. For example, the developer canbe sprayed onto the patterned coating material. Also, spin coating canbe used. For automated processing, a puddle method can be used involvingthe pouring of the developer onto the coating material in a stationaryformat. If desired, spin rinsing and/or drying can be used to completethe development process. Suitable rinsing solutions include, forexample, ultrapure water, methyl alcohol, ethyl alcohol, propyl alcohol,4-methyl-2-pentanol and combinations thereof.

As noted above, the prior method to improve adhesion and patternperformance on silicon (Si), e.g., amorphous silicon (α-Si), crystallinesilicon (c-Si), and combinations thereof, or silicon oxide. e.g., lowtemperature oxide (LTO) substrates was priming the surface to bepatterned with hexamethyldisazane (HMDS). As noted above, it has beendetermined that resist adhesion under these circumstances is marginalfor resolution patterning in the sub 40 nm pitch realm (sub-40P). Thisis especially the case for photoresist layers developed usingtetramethyl ammonium hydroxide (TMAH). It has been determined that usingthe methods described above, amorphous silicon (α-Si) or crystallinesilicon (c-Si) can be stripped off their native oxide, e.g., siliconoxide, without HDMS using the an HF-based chemical, such as dilute HF,thereby converting the terminal surface functionality tosilicon-hydrogen bonds. It has further been determined that thesilicon-hydrogen bonded surface can be converted to a hydrophobicorganic surface, i.e., polar surface, by the application of a vaporpriming agent 17 a, 17 b based on alkynes (C—C triple bond), alcohols(ROH), or a combination thereof. The formation of the hydrophobicorganic surface provides for increased adhesion and fidelity ofpatterned photoresist layers developed using tetramethyl ammoniumhydroxide (TMAH).

FIG. 9 is a scanning electron microscope (SEM) image of a developedresist that was formed on an amorphous silicon surface that was treatedwith a dilute hydrofluoric acid (dHF) rinse followed by applying a vaporpriming agent to convert the silane terminated surface to a hydrophobicorganic surface prior to forming the photoresist layer. The imagedepicted in FIG. 9 was provided by an amorphous (α-Si) layer that wastreated with dilute hydrofluoric acid (dHF) to generate the SiHterminated surface. Subsequently, the surface was primed with3,5-dimethyl-1-hexyn-3-ol (an alkyn-ol known under the commercialtradename “Surfynol 61”) at 150° C. and atmospheric pressure with N₂carrier gas, prior to coating of an EUV resist and e-beam patterningwith TMAH development. The photoresist patterned on the alkynol-primedaSi surface illustrated good feature printability.

Referring to FIG. 1, following development of the lithographicallypatterning the photoresist layer, the method may continue with etchingthe underlying amorphous semiconductor layer 10 at step 6, asillustrated in FIG. 10. The etch process for etching the underlyingsemiconductor layer 10 is selective to the remaining portions of thephotoresist layer 20 b that provide a photoresist mask. As used herein,the term “selective” in reference to a material removal process denotesthat the rate of material removal for a first material is greater thanthe rate of removal for at least another material of the structure towhich the material removal process is being applied. For example, in oneembodiment, a selective etch may include an etch chemistry that removesa first material selectively to a second material by a ratio of 100:1 orgreater.

In one embodiment, the semiconductor layer 10 may be etched using ananisotropic etch. As used herein, an “anisotropic etch process” denotesa material removal process in which the etch rate in the directionnormal to the surface to be etched is greater than in the directionparallel to the surface to be etched. The anisotropic etch may bereactive ion etching (RIE). Reactive Ion Etching (RIE) is a form ofplasma etching in which during etching the surface to be etched isplaced on the RF powered electrode. Moreover, during RIE the surface tobe etched takes on a potential that accelerates the etching speciesextracted from plasma toward the surface, in which the chemical etchingreaction is taking place in the direction normal to the surface. Otherexamples of anisotropic etching that can be used at this point of thepresent invention include ion beam etching, plasma etching or laserablation.

In some embodiments, the semiconductor layer 10 is etched to provide anultrathin, e.g., less than 5 nm thick, patterned inorganic hardmask.e.g., a patterned inorganic hardmask composed of amorphous silicon(α-Si). The methods and structures disclosed herein may also be used toform a patterned hard mask that is composed of low temperature oxide(LTO) material.

The methods and structures described herein provide better resistthickness budget, higher etch selectively, lower line width roughness(LWR), improved defectivity, and increased wet strippability ofmaterials used in photolithography processes.

Reference in the specification to “one embodiment” or “an embodiment”,as well as other variations thereof, means that a particular feature,structure, characteristic, and so forth described in connection with theembodiment is included in at least one embodiment. Thus, the appearancesof the phrase “in one embodiment” or “in an embodiment”, as well anyother variations, appearing in various places throughout thespecification are not necessarily all referring to the same embodiment.

The present embodiments can include a design for an integrated circuitchip, which can be created in a graphical computer programming language,and stored in a computer storage medium (such as a disk, tape, physicalhard drive, or virtual hard drive such as in a storage access network).If the designer does not fabricate chips or the photolithographic masksused to fabricate chips, the designer can transmit the resulting designby physical means (e.g., by providing a copy of the storage mediumstoring the design) or electronically (e.g., through the Internet) tosuch entities, directly or indirectly. The stored design is thenconverted into the appropriate format (e.g., GDSII) for the fabricationof photolithographic masks, which typically include multiple copies ofthe chip design in question that are to be formed on a wafer. Thephotolithographic masks are utilized to define areas of the wafer(and/or the layers thereon) to be etched or otherwise processed.

Methods as described herein can be used in the fabrication of integratedcircuit chips. The resulting integrated circuit chips can be distributedby the fabricator in raw wafer form (that is, as a single wafer that hasmultiple unpackaged chips), as a bare die, or in a packaged form. In thelatter case, the chip is mounted in a single chip package (such as aplastic carrier, with leads that are affixed to a motherboard or otherhigher level carrier) or in a multichip package (such as a ceramiccarrier that has either or both surface interconnections or buriedinterconnections). In any case, the chip is then integrated with otherchips, discrete circuit elements, and/or other signal processing devicesas part of either (a) an intermediate product, such as a motherboard, or(b) an end product. The end product can be any product that includesintegrated circuit chips, ranging from toys and other low-endapplications to advanced computer products having a display, a keyboardor other input device, and a central processor.

It should also be understood that material compounds will be describedin terms of listed elements, e.g., SiGe. These compounds includedifferent proportions of the elements within the compound, e.g., SiGeincludes Si_(x)Ge_(1-x) where x is less than or equal to 1, etc. Inaddition, other elements can be included in the compound and stillfunction in accordance with the present principles. The compounds withadditional elements will be referred to herein as alloys.

It is to be appreciated that the use of any of the following “/”,“and/or”, and “at least one of”, for example, in the cases of “A/B”. “Aand/or B” and “at least one of A and B”, is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of both options (A andB). As a further example, in the cases of “A, B, and/or C” and “at leastone of A, B, and C”, such phrasing is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of the third listedoption (C) only, or the selection of the first and the second listedoptions (A and B) only, or the selection of the first and third listedoptions (A and C) only, or the selection of the second and third listedoptions (B and C) only, or the selection of all three options (A and Band C). This can be extended, as readily apparent by one of ordinaryskill in this and related arts, for as many items listed.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of exampleembodiments. As used herein, the singular forms “a,” “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises,” “comprising,” “includes” and/or “including,” when usedherein, specify the presence of stated features, integers, steps,operations, elements and/or components, but do not preclude the presenceor addition of one or more other features, integers, steps, operations,elements, components and/or groups thereof.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper,” and the like, can be used herein for ease of description todescribe one element's or feature's relationship to another element(s)or feature(s) as illustrated in the FIGS. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the FIGS. For example, if the device in theFIGS. is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the term “below” can encompass both an orientation ofabove and below. The device can be otherwise oriented (rotated 90degrees or at other orientations), and the spatially relativedescriptors used herein can be interpreted accordingly. In addition, itwill also be understood that when a layer is referred to as being“between” two layers, it can be the only layer between the two layers,or one or more intervening layers can also be present.

It will also be understood that when an element such as a layer, regionor substrate is referred to as being “on” or “over” another element, itcan be directly on the other element or intervening elements can also bepresent. In contrast, when an element is referred to as being “directlyon” or “directly over” another element, there are no interveningelements present. It will also be understood that when an element isreferred to as being “connected” or “coupled” to another element, it canbe directly connected or coupled to the other element or interveningelements can be present. In contrast, when an element is referred to asbeing “directly connected” or “directly coupled” to another element,there are no intervening elements present.

It will be understood that, although the terms first, second, etc. canbe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another element. Thus, a first element discussed belowcould be termed a second element without departing from the scope of thepresent concept.

Having described preferred embodiments of a device and method (which areintended to be illustrative and not limiting), it is noted thatmodifications and variations can be made by persons skilled in the artin light of the above teachings. It is therefore to be understood thatchanges may be made in the particular embodiments disclosed which arewithin the scope of the invention as outlined by the appended claims.Having thus described aspects of the invention, with the details andparticularity required by the patent laws, what is claimed and desiredprotected by Letters Patent is set forth in the appended claims.

What is claimed is:
 1. A method of forming a semiconductor devicecomprising: removing an oxide containing surface layer from asemiconductor surface that is to be patterned with a fluoride basedchemistry, wherein applying the fluoride based chemistry to the surfaceto be patterned forms a terminated surface; applying a priming agentbearing chemical functionality based on alkynes to convert theterminated surface to a hydrophobic organic surface; patterning aphotoresist layer on the hydrophobic organic surface; and etching thesemiconductor surface using the photoresist layer that is patterned toprovide the semiconductor device.
 2. The method of claim 1, wherein saidpatterning is a lithography method using EUV lithography.
 3. The methodof claim 1, wherein said patterning is a lithography method using E-beamlithography.
 4. The method of claim 1, wherein the semiconductor surfaceis comprised of a type IV semiconductor material.
 5. The method of claim1, wherein the semiconductor surface comprises amorphous silicon.
 6. Themethod of claim 1, wherein said vapor priming agent bearing chemicalfunctionality based on alkynes to convert the terminated surface to ahydrophobic organic surface comprises an alkyne selected from the groupconsisting of 5-chloro-1-pentyne, Propargyl ether, Iodo-1-pentyne,5-Hexynoic acid, 1,7-Octadiyne, Ethyl propiolate, Dimethylpropargylmalonate, Methyl propiolate, 1-Hexyne, 1-Octyne, andcombinations thereof.
 7. The method of claim 1, wherein the forming thephotoresist layer comprises spin on deposition.
 8. The method of claim1, wherein the developing patterned portions of the photoresistcomprises TMAH.
 9. The method of claim 1, wherein the semiconductordevice is a field effect transistor.
 10. A method of forming asemiconductor device comprising: removing an oxide containing surfacelayer from a semiconductor surface that is to be patterned with afluoride based chemistry, wherein applying the fluoride based chemistryto the surface to be patterned forms a terminated surface; applying apriming agent bearing chemical functionality based on alcohols toconvert the terminated surface to a hydrophobic organic surface;patterning a photoresist layer on the hydrophobic organic surface; andetching the semiconductor surface using the photoresist layer that ispatterned to provide the semiconductor device.
 11. The method of claim10, wherein said patterning is a lithography method using EUVlithography.
 12. The method of claim 10, wherein said patterning is alithography method using E-beam lithography.
 13. The method of claim 10,wherein the semiconductor surface is comprised of a type IVsemiconductor material.
 14. The method of claim 13, wherein thesemiconductor surface is comprised of silicon.
 15. The method of claim10, wherein the semiconductor surface comprises amorphous silicon. 16.The method of claim 10, wherein said vapor priming agent bearingchemical functionality based on alkynes to convert the terminatedsurface to a hydrophobic organic surface comprises an alcohol selectedfrom the group consisting of 2-Propyn-1-ol, 3-Butyn-1-ol, 4-Pentyn-1-ol,1-Hexyn-3-ol, 4-Pentyn-2-ol, 1-Pentyn-3-ol, 4-Methyl-1-heptyn-3-ol,5-Hexyn-3-ol, 1-Octyn-3-ol, 3-Butyn-2-ol, 3,5-Dimethyl-1-hexyn-3-ol,2-Methyl-3-butyn-2-ol, 3-Methyl-1-pentyn-3-ol, 3-Ethyl-1-pentyn-3-ol,1-Ethynylcyclopentanol and combinations thereof.
 17. The method of claim10, wherein the forming the photoresist layer comprises spin ondeposition.
 18. The method of claim 10, wherein the developing patternedportions of the photoresist comprises TMAH.
 19. The method of claim 10,wherein the semiconductor device is a field effect transistor.
 20. Themethod of claim 10, wherein the etching the semiconductor surfacecomprises an anisotropic etch.